1. Field of the Invention
The present invention relates to an ultrasonic wave medical treatment for treating treatment targets such as tumors, calculi, etc. inside a living body by applying ultrasonic waves thereon.
2. Description of the Background Art
In recent years, for a treatment of the calculosis, much attention has been attracted to a lithotriptor for destroying calculi inside a living body non-invasively by applying intense ultrasonic waves focused on the calculi to be destroyed in the living body.
For a source of the intense ultrasonic waves to be used in such a lithotriptor, there are many conventionally known sources including a source using a spark discharge in water, a source using an electromagnetic induction, a source using a small scale explosion, and a source using piezoelectric elements, each of which has its own advantages and disadvantages. Among them, the source using piezoelectric elements is known to have the disadvantage that the intensity of the ultrasonic waves at the focal point is rather small, but this type of source is also known to have several excellent advantages including the smallness of the size of the focal point, the elimination of the consumption, the controllability of the intense ultrasonic waves, the controllability of the position and the shape of the focal point by phase controlling the driving waveforms to be applied to a plurality of piezoelectric elements. (See, Japanese Patent Application Laid Open No. 60-145131. U.S. Pat. No. 4,526,168, and Japanese Patent Application Laid Open No. 62-42773.)
On the other hand, for a treatment of cancer, much attention has been attracted to a hyperthermia treatment which treats the cancer by utilizing the fact that the tumor tissues have higher thermal sensitivity than the normal tissues such that they can be killed by heating them at the temperature higher than 42.5.degree. C. In such a hyperthermia, the localized heating of the tumor portion is known to be particularly effective.
For a heating method to be used in such a hyperthermia, the method utilizing the electromagnetic waves such as microwaves has been used conventionally. However, this conventional method of heating has a difficulty in selectively heating the tumor located deep inside the living body because of the electrical characteristics of the living body that affect the penetration of the electromagnetic waves, so that the satisfactory level of treatment has been realized only for the relatively superficial tumors located within 5 cm from the surface of the living body.
For this reason, for a treatment of the deeply located tumors, there has been a proposition to use a heating method utilizing the acoustic energy such as ultrasonic waves which utilizes the fact that the ultrasonic waves have superior focusing ability as well as deeper penetration range.
There is also a proposition for a treatment method in which the above described hyperthermia is further developed to burn the tumor tissues to death by heating the tumor portion at the temperature higher than 80.degree. C., as disclosed in Japanese Patent Application No. 3-306106.
For a source of the ultrasonic waves to be used in such a hyperthermia using the ultrasonic waves, the conventionally proposed sources include an ultrasonic transducer constructed from a plurality of piezoelectric elements which has an overall spherical surface, and an annular array ultrasonic transducer constructed by arranging a plurality of ring shaped ultrasonic transducer elements concentrically. Among them, the annular array ultrasonic transducer has the advantage that the depth of the focal point can be varied electrically.
There is also a proposition for the phased array ultrasonic transducer in which the position of the focal point can be moved three-dimensionally, as disclosed in U.S. Pat. No. 4,526,168.
There is also a proposition for the treatment apparatus in which the above described lithotriptor is provided along the above described hyperthermia integrally, as disclosed in Japanese Patent Application No. 3-306106.
There is also a proposition for a hyperthermia treatment apparatus incorporating an ultrasonic wave source using piezoelectric elements in which the treatment target portion can be heated uniformly by utilizing the small focal point characteristic to the ultrasonic wave source using piezoelectric elements, as disclosed in Japanese Patent Application Laid Open No. 61-209643.
However, in this hyperthermia treatment apparatus, the focal point is moved continuously such that the ultrasonic waves are applied to neighboring regions sequentially. Consequently, it has been impossible in this hyperthermia treatment apparatus to carry out the treatment procedure including the application of the ultrasonic waves to two distanced points alternately or the avoidance of obstacles such as bones during the application of the ultrasonic waves, so that there is a danger of damaging the normal tissues in vicinities of the tumor tissues.
Moreover, in a case of applying the intense ultrasonic waves continuously at a fixed target position, the acoustic energy released immediately after the start of the application of the ultrasonic waves can reach to the target position without any obstruction, but the acoustic energy reaching to the target position will be gradually attenuated as air bubbles generated at or in vicinity of the focal point due to the cavitation caused by the intense ultrasonic waves themselves start to reflect the intense ultrasonic waves. The same problem due to the cavitation is also present in a case of applying the intense ultrasonic waves by moving the focal point slowly.
Here, the cavitation is the phenomenon in which the air bubbles (air cavities) are generated by tearing off the water through which the intense ultrasonic waves pass, as a very large tensile force is exerted to the water due to the influence of the negative pressure associated with the intense ultrasonic waves passing through the water. The air bubbles so generated will subsequently function as reflectors for the ultrasonic waves. Consequently, when a large amount of air bubbles generated by the cavitation are floating around the previous focal points to which the intense ultrasonic waves have already been applied, the acoustic energy of the intense ultrasonic waves applied to a new focal point in a vicinity of the previous focal points will be attenuated.
On the other hand, in a conventional hyperthermia treatment apparatus, the positioning of the focal point is achieved by utilizing the two-dimensional ultrasound tomographic images. However, the tumor to be treated very often has a complicated three-dimensional shape in practice, so that it has been very difficult to realize the complete treatment of the entire tumor by using the two-dimensional tomographic images.
To cope with this problem, there has been a proposition to utilize the three-dimensional ultrasound images, as disclosed in Japanese Patent Application Laid Open No. 61-209643.
However, in the ultrasound images, the region behind the bones and the pneumatic organs such as a lung becomes invisible, so that the full three-dimensional information cannot be provided, and only the relative position of the focal point and the treatment target portion can be ascertained at best.
Furthermore, such a conventional hyperthermia treatment apparatus has no means to judge the effect of the treatment made, so that whether to continue or discontinue the treatment cannot be decided over a considerably long period of time ranging from several weeks to several months required to ascertain the effect of the treatment by some conventionally known methods.
Moreover, it has been difficult in the conventional hyperthermia treatment apparatus to accurately determine the temperature at which the tumor portion is actually heated, so that it has been difficult to prevent the accidental overlooking of some tumor portions to be treated or the excessive heating of some portions to which the intense ultrasonic waves are applied.